Automotive fluid tubing, especially for fuel and hydraulic fluid

ABSTRACT

An automotive fluid tubing, especially for gasoline, diesel fuel or hydraulic fluid, and composed of metal can be provided with a tube coating of aluminum and then a polyamide 12 layer which is extruded onto the aluminum coating. The polyamide extruded layer greatly improves the wear-resistance and corrosion-resistance of the tubing.

FIELD OF THE INVENTION

[0001] Our present invention relates to an automotive vehicle tubingintended especially for use with liquids common in automotiveapplications such as fuel (gasoline or diesel fuel) and hydraulic fluidsuch as brake fluid. More particularly, the invention relates to tubingfor such purposes wherein a metallic inner tube has an aluminum tubingand a polyamide layer on such coating.

BACKGROUND OF THE INVENTION

[0002] Automotive vehicle tubing of the type described is designed tominimize corrosion and abrasive wear and, therefore, to be capable ofuse where the tubing is exposed to the elements, for example, on theunderside of a vehicle chassis.

[0003] The aluminum coating may additionally have a chromate coatingbetween the polyamide layer and the aluminum and in the past thepolyamide or nylon coating has been composed of polyamide-11 (nylon-11)applied as a powder coating. In practice it has been found that thecorrosion-resistance and abrasion-resistance of such tubing can befurther improved.

OBJECTS OF THE INVENTION

[0004] It is, therefore, the principal object of the present inventionto provide an improved automotive vehicle tubing, especially for usewith automotive vehicle fuels and hydraulic fluids in which thecorrosion-resistance and abrasion-resistance are enhanced.

[0005] Another object of this invention is to provide a tubing for thepurposes described but which is free from drawbacks of earlier compositetubing.

SUMMARY OF THE INVENTION

[0006] These objects are achieved, in accordance with the invention, byproviding a polyamide or nylon layer of polyamide-12 or nylon 12 whichis extruded onto the aluminum coating. More particularly, the automotivefluid tubing of the present invention can comprise:

[0007] a metallic inner pipe;

[0008] an aluminum coating on an exterior of the inner pipe; and

[0009] a polyamide-12 layer extruded onto and bonded to the aluminumcoating.

[0010] The term “polyamide-12” is used here interchangeably with nylon12.

[0011] Surprisingly, the combination of an aluminum coating on themetallic inner pipe and a polyamide-12 layer extruded onto and aroundthe aluminum coating can provide a substantially betterabrasion-resistance than has been obtainable heretofore. Indeed, testshave shown that with automotive vehicle tubing of the invention animprovement in abrasion-resistance by at least 30% can be obtained.

[0012] The inner pipe can be composed of steel and can be fabricated ina simple manner, e.g. by rolling a steel strip through 360° and weldingthe abutment edges together with a longitudinal butt-weld seam.Alternatively, a doubly rolled inner pipe can be fabricated in which thestrip is rolled through 720° and where two turns of the rolled pipe arejoined by soldering. The metallic inner pipe can have a wall thicknessof 0.2 to 8 mm, preferably 0.4 to 1.5 mm.

[0013] According to a feature of the invention the aluminum coating is ahot-dip aluminum coating formed by passing the metal pipe through analuminum melt which completely wets the external surface of the innerpipe. Excess melt is blown off by gas jet and the layer thickness of thehot-melt aluminum coating is controlled to be 50 to 200 μm, preferably100 to 140 μm.

[0014] The polyamide-12 layer can also include substances for enablingthe electrostatic bonding thereof at its inner side to the outer surfaceof the tube and the additives for that purpose can include conductivecarbon black, graphite fibers and/or carbon fibers. The polyamide-12layer should have a thickness of 50 to 200 μm, preferably 100 to 140 μm.

[0015] According to a further feature of the invention, the aluminumcoating can be provided with a chromium-free surface treatment layer,especially a phosphatizing coating and/or a primer coating which will bedisposed between the aluminum coating and the polyamide-12 layer. Thesecoatings increase the corrosion and wear-resistance and particularlyimprove the adhesion of the polyamide-12 layer to the metal pipe.

[0016] The chromium-free surface treatment coating can have a thicknessof 0.2 to 0.8 μm and is preferably small than 0.5 μm. The primer coatingcan have a thickness of 1 to 8 μm, preferably 3 to 5 μm. Because theproduct may be subject to mechanical and thermal stress when in placeand when being installed in an engine compartment or on the underside ofthe chassis, and to reduce noise produced by the tubing, on the outerside of the polyamide-12 layer a protective layer of a thermoplasticelastomer or polypropylene can be applied. The coating can have athickness of 1 to 3 mm, preferably 1.5 to 2 mm.

BRIEF DESCRIPTION OF THE DRAWING

[0017] The above and other objects, features, and advantages will becomemore readily apparent from the following description, reference beingmade to the accompanying drawing in which:

[0018]FIG. 1 is a cross sectional view through the various layers of atubing for fuel or hydraulic fluid in an automotive vehicle;

[0019]FIG. 2 is a cross sectional view through the inner metal pipe inaccordance with one embodiment of the invention;

[0020]FIG. 3 is a cross sectional view through the inner pipe inaccordance with a second embodiment; and

[0021]FIG. 4 is a side elevational view illustrating the extrusion ofthe polyamide-12 layer onto the aluminum coated metal pipe.

SPECIFIC DESCRIPTION

[0022] From FIG. 1 it will be apparent that the metallic inner pipe 1,namely, a steel pipe in the form of a simply rolled and longitudinallyseen pipe with a butt-weld seam, an outer diameter of 4.68 mm and a wallthickness of 0.7 mm can form the inner member of the automotive fluidtubing.

[0023] On the outer side of this inner pipe 1 a hot-dipped aluminumcoating 2 of a thickness of about 120 μm is applied. On the aluminumcoating 2 a chrome-free surface treatment layer 3 in the form of aphosphate coating is applied with a thickness of say 0.4 μm on thephosphate coating 3, a 5 μm thick primer coating 4 of a commercial nylonprimer is applied. A polyamide-12 layer 5 of 120 μm is extruded onto theprimer coating and can be covered by a protective layer of a thicknessof about 2 mm of a thermoplastic elastomer or polypropylene. This layeris designated as 6.

[0024]FIG. 2 shows that the pipe 1 can be bent from a steel strip sothat its edges 7, 8 are juxtaposed to allow a longitudinal weld seam 9to be formed between the edges. Alternatively, the steel pipe 1′ (FIG.3) may be made by rolling the strip through, say, 720° and providing asolder layer 10 between the turns.

[0025] As can be seen in FIG. 4, the pipe is passed through an extruderhead 11 to enable the polyamide layer 5 to be extruded therearound.

We claim:
 1. An automotive-fluid tubing comprising: a metallic innerpipe; an aluminum coating on an exterior of said inner pipe; and apolyamide-12 layer extruded onto and bonded to the aluminum coating. 2.The automotive-fluid tubing defined in claim 1 wherein said inner pipeis a steel pipe.
 3. The automotive-fluid tubing defined in claim 1wherein said metallic inner pipe is a rolled pipe having a weldedlongitudinal seam between butting edges.
 4. The automotive-fluid tubingdefined in claim 1 wherein said metallic inner pipe is a doubly rolledpipe having solder extending around said pipe between layers thereof. 5.The automotive-fluid tubing defined in claim 1 wherein said metallicinner pipe has a wall thickness of 0.2 to 8 mm.
 6. The automotive-fluidtubing defined in claim 5 wherein said wall thickness is 0.4 to 1.5 mm.7. The automotive-fluid tubing defined in claim 1 wherein said aluminumcoating is a hot-dip coating.
 8. The automotive-fluid tubing defined inclaim 7 wherein said coating has a thickness of 50 to 200 μm.
 9. Theautomotive-fluid tubing defined in claim 8 wherein said thickness is 100to 140 μm.
 10. The automotive-fluid tubing defined in claim 1 whereinsaid polyamide-12 layer contains a conductive additive rendering saidpolyamide-12 layer electrically conductive.
 11. The automotive-fluidtubing defined in claim 1 wherein said polyamide-12 layer has athickness of 50 to 200 μm.
 12. The automotive-fluid tubing defined inclaim 11 wherein said thickness is 100 to 140 μm.
 13. Theautomotive-fluid tubing defined in claim 1 wherein at least oneintervening layer selected from the group which consists of achromium-free surface-treatment layer and a primer layer is disposedbetween said aluminum coating and said polyamide-12 layer.
 14. Theautomotive-fluid tubing defined in claim 13 wherein said chromium-freesurface-treatment layer is a phosphatization coating.
 15. Theautomotive-fluid tubing defined in claim 13 wherein said chromium-freesurface-treatment layer has a thickness of 0.2 to 0.8 μm.
 16. Theautomotive-fluid tubing defined in claim 15 wherein said chromium-freesurface-treatment layer has a thickness which is smaller than 0.5 μm.17. The automotive-fluid tubing defined in claim 12 wherein said primerlayer is of a thickness of 1 to 8 μm.
 18. The automotive-fluid tubingdefined in claim 17 wherein said primer layer has a thickness of 3 to 5μm.
 19. The automotive-fluid tubing defined in claim 1, furthercomprising a protective layer of a thermoplastic elastomer or ofpolypropylene on an outside of said polyamide-12 layer.
 20. Theautomotive-fluid tubing defined in claim 19 wherein said protectivelayer has a thickness of 1 to 3 mm.
 21. The automotive-fluid tubingdefined in claim 20 wherein said thickness is 1.5 to 2 mm.
 22. A methodof making an automotive-fluid tubing for brake fluid or hydraulic fluid,comprising the steps of: (a) forming a metallic inner pipe of a wallthickness of 0.2 to 8 mm by rolling and butt-welding rolled edges toform a longitudinal seam or doubly rolling the metallic inner pipe andapplying solder around said pipe and between layers thereof; (b) hot dipcoating said metallic inner pipe to form an aluminum coating of athickness of 50 to 200 μm thereon; (c) applying at least one interveninglayer selected from the group which consists of a chromium-freesurface-treatment layer and a primer layer to said aluminum coating; (d)extruding onto said at least one intervening layer a 50 to 200 μm thicklayer of polyamide-12; and (e) applying to the layer of polyamide-12 a 1to 3 mm thick protective layer of a thermoplastic elastomer or apolypropylene.